1 THE  PREPARATION  OF 
ANHYDROUS  OXALIC  ACID 

II  A NEW  METHOD  FOR  THE 
PREPARATION  OF  FURFURAL 


BY 


VANDRRVEER  VOORHEES 


THESIS 

FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIENCE 
IN 

CHEMICAL  ENGINEERING 


COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 

UNIVERSITY  OF  ILLINOIS 


1921 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/preparationofanhOOvoor 


UNIVERSITY  OF  ILLINOIS 


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TAPLE  OF  CONTENT? 


I Anhydrous  Oxalic  Acid 
Introduction 
Experirr.ental 
Di scussion 

Drawings  of  Apparatus 
II  Furfural 

Introduction 
Di scussion 
Experimental 
Notes 

Conclusion 
Summary 
Bibliography 
Drawings  of  Apparatus 


Page 

1 

3 

6 

Appendix  A. 

10 

12 

14 

21 

22 

23 

25 

Appendix  B. 


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1 


INTRODUCTION 

Certain  organic  reactions,  such  as  the  preparation  of  oxalic 
esters,  require  oxalic  acid  entirely  free  from  water.  Since  the 
pure,  crystallized  acid  contains  two  molecules  of  water  of  crystal- 
lization, this  must  he  removed  before  the  acid  may  be  used  for 
these  purposes. 

Oxalic  acid  cannot  be  satisfactorily  dried  in  an  ordinary  oven, 

since  it  sublimes  arpreciably  at  temperatures  below  100©,  and  above 

(1)  (2) 

this  temperature  decomposition  ensues.  Beilstein  mentions  that 
the  water  of  crystallization  may  be  removed  by  standing  over  cone. 
HgSO*,  but  it  is  obvious  that  this  method  would  not  be  applicable 
to  the  preparation  of  any  considerable  quantity. 

In  order  to  overcome  the  above  difficulties.  Dr.  H.  T.  Clarke, 
of  the  Eastman  Kodak  Co.  h&s  devised  the  following  process  (as  yet 
unpublished)  which  may  be  carried  out  in  any  laboratory.  Finely 
crystallized  oxalic  acid  is  boiled  with  CCI4,  the  vapor  of  which 
carries  out  the  water  according  to  the  law  of  partial  pressures. 

The  vapors  are  condensed  into  a gravity  separator  where  the  water 
flows  off  and  the  CCI4  is  returned  to  the  flask.  This  is  continued 
until  all  water  has  been  distilled  out,  the  product  being  obtained 
by  filtering  off  the  CCI4,  the  last  of  which  is  removed  in  a 
current  of  dry  air. 


(1)  Gay  Lussac,-  Ann.  Chera.  1-30, 
(3)  Handbuch  - 1 - 639. 


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The  purpose  of  this  research  was  to  check  over  the  above  metho: 
and  determine  the  most  suitable  form  of  apparatus  to  use;  one 
which  would  give  the  least  loss  of  CCI4  and  dry  the  acid  in  the 
shortest  time.  Previous  work  with  this  method  showed  that*^large  I 
loss  of  CCI4  could  not  be  avoided,  thus  making  the  process  an 
expensive  one.  To  determine  where  this  loss  occurred,  a number 
of  experiments  were  made  with  different  forms  of  apparatus,  the 
loss  of  CCI4  being  observed  in  each  case. 

ETPERIMENTAL 

Experiment  1.  - Two  Kg.  C.  ?.  oxalic  acid  were  passed  through 
a 30-mesh  seive  and  placed  in  a 5-1.  round  bottom  flask  with  5 Kg. 
CCI4.  The  flask  was  fitted  with  a glass  stir  of  the  vdng  type 
reaching  almost  to  the  bottom  and  sealed  by  a column  of  mercury 
about  3 inches  deep.  Connection  was  made  to  the  top  of  a vertical 
condenser  by  a tube  50  inches  long  and  1/3  inch  diameter,  wrapped 
v;ith  asbestos  to  decrease  condensation.  The  condenser,  30  in.  long 
and  5/8  in.  diameter  was  connected  at  the  Icv/er  end  tc  the  water 
separator.  In  Dr.  Clarke's  apparatus  this  separation  was  effected 
by  means  of  a simple  trap  with  a funnel  set  into  it  to  catch  the 
liquid  from  the  condenser.  The  objection  to  this  is  the  large 
surface  offered  for  evaporation,  so  a modification  of  this  separator 
was  used  in  this  and  follcwing  experiments.  This  device,  shown  in 
Fig.  1,  consisted  of  a glass  tube  8 in.  long  and  7/8  in.  Ham.  with 
a small  tube  sealed  at  the  side  for  a water  overllow  and  a second 
small  tube  leading  up  from  the  bottom  to  within  1/4  in.  of  the  water 


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outlet  where  it  was  bent  horizontally  and  connected  to  the  flask. 
This  maintained  the  level  of  CCI4  just  below  that  of  the  water 
outlet,  and  the  water,  being  much  lighter,  collected  on  the  surface 
until  the  layer  became  sufficient  to  reach  the  overflow  where  it 
ran  out  and  was  collected  in  a covered  beaker. 

The  connection  between  the  separator  and  the  conienser  was 
arranged  with  a capillary  open  to  the  air  to  maintain  atmosp'heric 
pressure  and  insure  the  proper  adjustment  of  the  liquid  levels. 

For  this  reason  also,  the  return  tube  was  made  'with  an  enlargement 
containing  a capillary  to  prevent  siphoning  the  contents  out  of 
the  separator  into  the  flask  during  operation.  The  returning  CCI4 
was  delivered  by  a small  tube  extending  well  below  the  surface  of 
the  mixture  in  the  flask  to  prevent  vapor  rising  and  escaping 
through  this  last  mentioned  capillary.  A small  funnel  was  sealed 
within  the  separator  just  below  the  condenser  to  deliver  the  00X4 
below  the  surface  and  prevent  its  being  floated  out  with  the  water 
by  surface  tension. 

Corks  were  used  at  the  condenser  connections,  but  a rubber 
stopper  was  used  at  the  flask,  owing  to  the  difficulty  of  making 
a large  cork  stopper  carrying  two  tubes  and  a stir,  sufficiently 
vapor  tight.  Hovirever,  the  rubber  was  abandoned  at  the  end  of  this 
run  as  it  was  found  impossible  to  prote  ct  it  from  the  solvent 
action  of  the  tetrachloride,  altho  tinfoil  and  collodion  laquer 
ware  both  tried.  The  rubber  also  showed  a tendency  to  discolor 
the  product. 


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Distillation  ovsr  a direct  flame  vias  carried  on  for  a total 
period  of  30  hrs.  At  this  time  the  CCI4  returning  to  the  flask 
had  lost  part  of  its  milkiness  due  to  entrained  water,  but  had  not 
become  clear.  Gome  trouble  was  occasioned  by  the  return  tube 
becoming  closed  at  the  end  by  an  agglomeration  of  oxalic  acid 
which  required  frequent  removal.  After  cooling,  the  acid  was 
filtered  off  by  suction  until  no  more  CCI4  could  be  obtained. 

The  remaining  CCI4  w2i.s  expelled  in  the  oven  at  lOO  , but  some 
sublimation  occurred  at  this  temperature,  causing  the  finely 
powdered  acid  to  sinter  together  into  a mass  of  delicate  needles. 

3900  g.  of  CCI4  was  recovered,  denoting  a loss  of  1100  g. 

1350  g.  of  anhydrous  acid  was  obtained,  which  is  94.5^  of 
the  theory.  The  loss  was  most  likely  due  to  sublimation  in  the 
oven.  Titration  of  the  product  showed  a water  content  of  less 
than  .01  mol.  HgO. 

Experiment  3.  - In  this  escperiment  several  changes  vyere  made 
in  the  apparatus.  The  length  of  the  separator  was  increased  from 
& in.  to  14  in.,  and  the  diameter  from  7/8  in.  to  1-3/8  in.  This 
was  done  to  allow  the  water  more  time  to  separate  before  the  CCI4 
was  returned  to  the  flask.  The  tube  returning  the  GCI4  was  ex- 
tended just  through  the  stopper  in  the  flask,  and  a loop  was  made 
in  it  to  prevent  the  reverse  passage  of  vapor.  In  this  way, 
plugging  of  the  end  of  the  return  tube  within  the  flask  was  effect- 
ually prevented,  A cork  stopper  was  used  in  the  flask  and  painted 
with  sodium  silicate  to  render  it  impervious  to  vapor.  The 


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capillaries  previously  mentioned  as  essential  to  the  working  of 
the  separator,  were  replaced  by  connections  to  a small  vertical 
condenser  as  sho'^n  in  the  sketch  to  prevent  any  escape  of  CCI4 
vapor.  The  small  funnel  which  was  selaed  vdthin  the  previous 
separator,  was  merely  rested  on  a constriction  of  the  wall  in 
this  one.  This  was  done  to  siiiplify  construction.  The  entire 
apparatus  is  shown  in  F'ig.  2,  and  was  used  in  succeeding  experi- 
ments. A water-bath  entirely  surrounding  the  flask  was  used  in 
this  experiment  in  place  of  direct  heat. 

2 Kg,  oxalic  acid  graded  as  before  and  5 Kg.  CCI4  were  placed 
in  the  flask.  Distillation  was  carried  on  for  a total  period  of 
18-1 /2  hrs,  2500  g.  of  CCI4  was  recovered  by  filtration  from  the 
anhydrous  acid,  showing  a loss  of  2500  g.  Part  of  this  loss  was 
due  to  clogging  of  the  return  tube  at  starting  and  overflow  of 
the  separator.  The  product  'Afas  freed  ffom  CCI4  by  spreading  on  a 
paper  placed  above  a radiator  for  a few  hours. 

1450  g.  of  anhydrous  aoid  va,s  obtained  which  is  a trifle  more 
than  the  theory  (l430  g.).  Allowing  for  .02  mol  of  water,  deter- 
mined  by  titration  as  before,  this  is  practically  a quantitative 
yield. 

The  use  of  the  ;vater  bath  effectually  prevented  the  formation 
of  a crust  of  acid  about  the  upper  part  of  the  flask,  this  having 
been  previously  observed  by  Dr.  Clarke. 

Experiment  3.  - The  apparatus  was  used  just  as  in  the  pre- 
ceeding  experiment  with  the  exception  of  the  water  bath.  It  was 
felt  that  the  slight  advantage  of  the  crust  prevention  was  more 


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than  offset  by  the  inconvenience  of  handling  such  a cumbersome 
water  bath  and  continually  supplying  v^ater  to  make  up  for  that 
lost  by  evaporation.  All  connections  were  wrapped  with  strips 
of  cloth  which  were  wired  on  and  painted  heavily  with  sodium 
silicate.  Very  good  seals  were  obtained  in  this  way.  The  extracted 
water  was  collected  in  a covered  beaker  and  measured  at  intervals. 

Distillation  was  carried  on  for  a total  period  of  16-1/3  hrs. 
Water  was  collected  as  follows; 

After  7 hrs.  - 360  cc. 

” 13  n - 465  " 
w 18“l/3"  “ 545  « 

The  theory  requres  570  cc.,  the  discrepancy  being  undoubtedly 
due  to  evaporation  from  the  beaker  during  operation. 

The  product  was  dried  on  the  radiator  as  before  and  the  theory 
yield  was  obtained  (1430  g.)  . Titration  showed  the  presence  of 
.03  mol.  water. 

Loss  of  CCI4  was  not  determined  in  this  run  because  of  an 
accident  which  occurred  during  operation. 

Experiment  4.  ~ This  run  was  made  largely  for  the  purpose 
of  checking  the  results  of  the  previous  run  and  determining  the 
loss  of  CCI4.  In  order  to  minimize  back  pressure  on  the  flask, 
a steam  jacket  was  placed  on  the  vapor  tube  leading  to  the  con- 
denser as  shown  in  the  sketch.  This  was  advised  by  Dr.  Clarke 
and  entirely  prevented  condensation  in  this  tube.  Apparently 
the  previous  losses  of  CCI4  were  principally  due  to  loss  of  vapor 
at  the  mouth  of  the  flask  and  around  the  mercury  seal  of  the  stir, 


j., 

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. 7 - 


and  consequently  any  increase  in  pressure  would  increase  these  vapoi 
losses  proportionately*  Greater  care  was  taken  to  inspire  a tight 
joint  at  the  flask,  the  stopper  being  painted  with  sodium  silicate 
both  inside  and  out  and  the  entire  joint  wrapped  with  cloth, 
securely  wired  and  painted  with  silicate  solution. 

Distillation  vvas  carried  out  for  a total  period  of  23-1/2  hrs. 
during  which  time  555  cc.  of  vvater  was  collected  as  follows: 

After  4-I/2  hrs.  - 120  c.c. 
n 13  n » 375  " 

w ie-l/2”  ~ 520  « 

« 23-1/3”  “ 555  « 

A decrease  in  volume  in  the  flask  during  operation,  of  about  500  c.c. 
results  from  the  removal  of  ’water.  The  anhydrous  acid  was  filtered 
off  and  as  much  CCI4  removed  as  possible  by  pressing  and  suction. 

3950  g.  CCI4  was  recovered.  The  product,  which  was  in  a 
damp  condition,  was  weighed  before  drying  to  determine  the  loss 
of  CCI4.  It  was  then  dried  on  the  radiator  as  before  for  a period 
of  3 hrs.  after  which  it  was  bottled  and  weighed. 

Yield  - 1420  g.,  practically  theoretical. 

Wt . before  drying  - 2350  g. 

” after  « - 1430 

Loss  of  CC14  due  to  drying  930  g. 

930  3 9 50  « 4880  g.  or  almost  5 Kg.,  the  amount  used. 

Titration  showed  the  presence  of  .03  mol  of  water.  Indications 
are  that  some  of  this,  at  least,  was  absorbed  while  expelling  the 




Xf" 


« 6 - 


last  of  the  CCI4  on  the  radiator,  the  humidity  being  fairly  high, 
at  the  time,  and  a slight  crust  being  formed  oer  the  surface  of 
the  acid  after  exposure.  It  is  to  be  noted  also  that  the  product 
from  the  first  run,  which  was  placed  in  the  oven  to  expel’^CCl4, 
contained  the  least  water  (.01  mol.) 

DI SOU?? ION 

The  success  of  Dr.  Clarke's  method  for  dehydrating  oxalic 
acid  is  quite  evidently  dependent  on  the  economy  of  carbon  tetra- 
chloride consunp tion,  for  it  ^ves  unquestionably  a pure,  dry 
product.  I believe  my  exr>eriments  have  shown  ;jU3t  where  the  losses 
of  CCI4  occurr,  and  the  manner  and  extent  to  which  they  may  be 
p re vented. 

The  apparatus  which  I employed  is  practically  100*^  efficient 
as  shown  in  the  last  experiment  in  regard  to  CCI4  retention.  The 
loss  of  CCI4  on  drying  of  the  product  is,  in  so  far  as  I can  see, 
unavoidable  on  a laboratory  scale.  This  loss  could,  however,  be 
greatly  minimized  if  some  form  of  pressing  machine  were  available. 
When  using  the  laboratory  type  of  suction  filter,  I think  one  may 
figure  on  a loss  of  CCI4  equal  to  50"^  of  the  weight  of  the  crystal- 
lized acid  used. 

The  most  undesirable  feature  of  the  apparatus  is  the  impos- 
sibility of  using  rubber  stopper  connections.  Sodium  silicate, 
as  I used  it,  adheres  to  the  flasks  and  tubes,  dr^'ing  in  horrey 
lumps  which  can  only  be  removed  by  prolonged  soaking  in  water. 

In  one  experiment  the  stepper  was  so  securely  cemented  to  the 


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- 9 - 

flask  that  it  had  to  be  cut  and  removed  in  pieces.  I see  no 
solution  to  this  difficulty  except  in  the  construction  of  special 
flasks  and  connections  of  glass  arranged  for  ground  joints  or 
mercury  seals. 

It  has  been  suggested  by  Dr.  Clarke  that  the  use  of  calcim 
chloride  to  dry  the  returning  CCI4  toward  the  end  of  the  reaction 
mig^t  considerable  shorten  the  time  of  operation  by  removing  the 
entrained  water.  This  was  considered  but  abandoned  because  of  the 
manipulation  and  loss  of  CCI4  which  it  would  entail,  esp^e daily 
as  the  drying  agent  could  only  be  of  use  during  the  last  3 or  3 
hrs.  and  I felt  that  this  saving  in  time  would  be  insufficient, 
particularly  as  the  apparatus  which  I employed  required  practically 
no  attention  while  running. 

I might  add  that  when  the  reaction  is  properly  controlled, 
the  second  condenser  is  unnecessary  and  that  the  capillary  arrange- 
ment described  in  the  first  experiment  is  quite  satisfactory. 


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6'ii, 


A NEW  ItETHOD 
for  the 


P REP j9 RATION  OF  FURFURAL 


10 


INTPODUCTTON 

Furfural  (furfuraldehyle,  furallehyde,  furfurole)  when  pure 
is  a colorless  oil,  slightly  heavier  than  water  'with  a boiling 
point  of  161® (Esilstein) . It  is  a cyclic  ether  aldehyde  having 
the  following  formula  with  all  the 

properties  of  an  aldehyde  and  many  of  the  properties  of  the  aro- 
matic series.  It  is  soluble  in  v;ater  to  the  extent  of  1 part  in 

11  at  13®  , (Beilstein)  and  considerably  more  than  this  at  higher 

(l) 

temperatures.  It  is  also  quite  volatile  'with  steam.  Cohen 
gives  its  formation  from  pentose  by  the  loss  of  3 molecules  of 
water. 

Occurrence  - A glance  in  the  literature  will  show  that 

furfural  occurrs  widely  scattered  among  the  processes  of  annlied 

(3) 

chemistry.  We  find  it  in  vdne,  beer  and  fuseloil  and  in  waste 

(3) 

products  from  sulfite  pulp  manufacture.  It  may  be  obtained  by 

(4)  (5)  (6)  (7) 

acid  hydrolysis  of  sugar  , bran,  lignin,  cellulose,  and  oxy- 
(S)  C9) 

cellulose  and  also  by  hydrolysis  of  bran  with  zinc  chloride. 

It  results  fromi  the  acid  hydrolysis  of  pentoses  (arabinose  and 

, (10) 

xylose)  and  pentosans  , this  reaction  being  employed  in  the 
laboratory  for  the  quantitative  estimation  of  these  carbohydrates. 
In  brief,  it  seems  to  result  from  the  acid  hydrolysis  of  a great 
varietv  of  vegetable  products. 

Preparation  - A great  many  processes  have  been  devised  for 
the  production  of  furfural,  a number  of  which  have  been  patented.. 
Almost  vvithout  exception  they  consist  of  some  form  of  hydrolysis, 


- 11  - 

(11) 

this  being  accomplished  in  some  cases  by  steam  under  pressure 

or  by  various  strengths  and  kinds  of  acids. 

The  laboratory  method  which  has  been  in  general  use  is 

(12) 

essentially  that  given  by  Eeilstein  as  follows;  bran  is  di  s- 

tilled  with  30“^  KgSO^,  the  distillate  containing  less  than  1*^  of 

the  oil  in  solution.  This  distillate  is  concentrated  by  saturation 

with  salt  and  redistillation,  half  the  volume  being  collected. 

The  first  of  the  distillate  is  most  concentrated  and  the  oil  will 

separate  at  first  and  later  relissolve.  In  practice  it  is  rem.oved 

as  soon  as  no  more  is  seen  to  separate  from  the  water.  After  each 

distillation,  the  water  solution  is  saturated  with  salt  and  re- 

distilled  as  before,  this  procedure  being  continued  until  all  has 

been  obtained  as  the  oil. 

(13) 

Stone  found  in  1691  that  a very  much  larger  yield  of  fur- 
fural could  be  obtained  from  corn  cobs  than  from  most  other  veg- 

(14) 

etable  substances.  Following  this,  Noyes  , gave  directions  for 
its  preparation  from  cobs  using  constant  boiling  (SO^)  HCl  as 
hydrolytic  agent.  During  1917-16,  considerable  quantities  were 
made  by  the  latter  method  at  the  University  (Dept.  Chem.  Mfrs.) 
Results  from  this  work  show  that  an  average  yield  of  10-12*^  of  the 
weight  of  air  dry  cobs  was  obtained  in  this  'way.  Also, for  each 
150  g,  of  oil,  approximately  30  1 . of  solution  had  to  be  distilled, 
which  required  an  average  of  15  hrs. 

Use  - At  present  the  demand  for  furfural  is  rather  a limited 
one.  It  is  used  as  a reagent  for  the  detection  of  aromatic  primary 
amines  and  has  been  suggested  as  dyestuff  intermediate.  Colors 


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- 12 


made  from  it,  however,  have  proven  fugitive  to  light*  Some  use 
hae  been  made  of  it  in  perfumery  and  as  a vermicide. 

DI  SOT  SION 

As  far  as  I am  aware,  no  method  has  yet  been  published  by 
which  furfural  can  be  obtained  from  vegetable  matter  without  the 
distillation  of  disproportionately  great  voliimes  of  water  (or  acid) 
and  the  subsequent  concentration  of  the  distillate.  This  pro- 
cedure is  necessitated  by  the  fact  that  the  distillation  must  be 
extended  over  a long  period  of  hours,  since  the  rate  of  hydrolysis 
is  only  moderate  at  100©.  The  distillation  m^ust  also  be  maintained 
quite  rapid  thruout  this  time  in  order  to  get  a good  yield,  and 
consequently  a large  volume  of  distillate  collects  and  must  be 
concentrated  to  obtain  the  furfural  in  solution.  Several  attempts 
which  I made  to  complete  the  hydrolysis  previous  to  distillation 
and  then  distill  off  the  furfural  'which  should  have  been  formed, 
proved  failures,  very  small  yields  being  obtained.  This  led  me  to 
believe  that  the  furfural  formed  in  the  acid  solution  is  in  turn 
destroyed  by  the  acid,  the  rate  of  this  reaction  being  naturally 
dependent  on  the  concentration  of  the  furfural.  Later  results 
have  also  borne  cut  this  theory.  It  may  readily  be  understood 
then,  that  if  one  wishes  to  obtain  a maximum  yield,  he  must  keep  the 
concentration  of  furfural  in  the  acid  solution  at  a minimum.  One 
way  of  effecting  this  is  by  rapid  distillation,  the  method  which 
has  been  commonly  used. 


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- 13  - 


I found  th2.t  this  sautne  result  could  be  obtained  by  the 
addition  of  a large  amount  of  salt  to  the  acid  mixture,  for  it  is 
well  known  that  furfural  is  more  volatile  from  a salt  solution 
than  from  pure  water.  In  this  way  it  is  driven  off  with  water 
vapor  at  a much  lower  concentration  than  when  acid  is  used  alone. 

This  "salting  out"  process,  then,  explains  why,  in  the  past, 
it  has  been  customary  to  use  relatively  high  concentrations  of 
acid.  Experiment  had  shown  that  low  acid  concentrations  gave  low 
yields  of  furfural.  It  may  now  be  seen  that  this  condition  was 
not  due  to  the  lack  of  hydrogen  ion  concentration  sc  much  as  to 
the  absence  of  the  "salting  out"  effect.  When  salt  is  used,  the 
acid  concentration  may  be  reduced  to  l/5  or  l/‘6  the  previous 
value,  and  it  appears  that  the  results  are  more  satisfactory, 
the  lowerthe  concentration.  This  is  just  what  one  would  expect, 
since,  by  the  use  of  salt,  the  acid  concentration  may  be  lowered 
as  wclll  as  the  furfural  concentration,  and  thus  still  more  decrease 
the  speed  of  the  reaction  which  destroys  the  product. 

With  the  knowledge  of  the  above  principles  and  by  the  use  of 
proper  condensing  arrangements,  I have  been  able  to  distil  the 
furfural  from  a corn-cob-acid  mixture,  separate  the  oil,  and  con- 
tinuously return  the  water  (together  with  the  furfural  in  solution) 
to  the  flask  where  it  is  used  over,  thus  making  a complete  cycle 
of  operations.  The  process  is  entirely  automiatic,  once  started, 
and  the  crude  furfural  (oil)  m;ay  be  drawn  off  from,  the  condenser 
directly,  thus  making  it  necessary  to  handle  no  water  whatsoever, 
and  totally  eliminating  the  laborious  procedure  of  concentrating 


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14  - 


large  vol^amea  of  iilute  solution.  Following  is  a "brsif  review 
of  the  experiments  which  I have  male.  A number  of  others  which 
I had  in  mind  could  not  be  performed  for  want  of  time, 

ETt^FRIWFNTAL, 

In  this  work  all  experiments  were  condiicted  with  cobs  of  the 
previous  year’s  crop  (1919)  of  yellow  corn.  The  corn  had  been 
shelled  only  a few  months  prior  to  the  date  of  this  research 
(Oct.  1,  1930).  The  cobs  were  ground  in  a coal  crusher  to  approx- 
imately the  size  of  a pea,  there  being  some  pelces  considerably 
larger  and  also  much  fine  bran-like  material.  Sulfuric  acid  used 
was  the  ordinary  C.  95^  acid.  Salt  used  was  the  crude  barrel 
product.  When  weight  of  cobs  is  given,  it  is  meant  air  dry,  ground 
cobs  (about  10*^',  moisture),  and  by  percent  of  H^SO^  is  meant  acid 
of  sp . gr . 1.84, 

Expe riment  1 ,-  To  study  the  effect  of  hydrolysis  of  the  cobs, 
previouB  to  distillation  by  the  ordinarv  method,  1200  g.  of  cobs 
were  placed  in  a 12-h  . flask  with  6 L,  SSf-*  KaSO*,  The  flask  was 
placed  on  a steam  cone  and  heated  for  36  hrs.,  intimate  mixture  of 
acid  and  cobs  being  maintained  by  occasional  shaking.  The  mixture 
was  distilled  with  a rapid  current  of  steam,  5 L.  of  distillate 
being  collected.  On  concentration  with  salt  this  yielded  about 
10  g.  of  oil. 

Experiment  3,-  This  exj^eriment  was  performed  in  order  to 
determine  if  hydrolysis  at  the  boiling  temperature  would  increase 
the  yield  of  furfural.  1500  g.  of  cobs  were  hydrolyzed  by  boiling 


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gently  under  a reflux  condenser  v,lth  7 L,  HgSO^  for  a long 
period  of  hours.  The  mixture  was  distilled  with  steam  as  before 
and  the  furfural  obtained  by  concentration.  Tbe  yield  was  still 
less  than  in  the  former  experiment. 

Experiment.  3.  - Suspecting  the  decomposition  of  the  product 
by  the  acid,  I made  an  attempt  in  this  experiment  to  effect  the 
hydrolysis  with  lower  acid  concentration.  1 Kg.  cobs  were  re~ 
fluxed  gently  vTith  5 L.  5^  HgS04  for  a period  of  42  hrs.  Steam 
distillation  was  then  used  to  bring  over  the  furfural  which  should 
have  been  formed,  and  2-1 /2  L.  of  distillate  were  collected.  Very 
little  oil  was  obtained  from  this  on  concentration. 

Experiment  4.  - In  Experiments  (2)  and  (3)  it  was  noted  that 
beads  of  furfural  collected  in  the  reflux  condenser  during  hydroly- 
sis. It  occurred  to  me  that  if  this  oil  could  be  kept  from  return- 
ing to  the  acid,  the  equilibrium  between  the  reaction  of  formation 
and  that  of  decomposition  of  furfural,  might  be  disturbed  in  the 
direction  of  its  production. 

To  accomplish  this  a small  trap,  shown  in  Fig.  1,  was  placed 
below  the  reflux  condenser,  thru  which  tdie  condensate  was  required 
to  flow  on  its  return  to  the  flask, 

1 Kg.  cobs  were  placed  in  the  12-L . flask  with  5-L.  lOio  H3SO4. 
To  this  was  added  2 K'g.  salt  for  the  purpose  previously  discussed. 
Heat  from  a large  ring  burner  was  applied  to  the  flask.  After  3 hrs 
of  refluxing,  40  g.  crude  oil  had  been  collected  in  the  trap  and 

was  removed.  7 hrs.  longer  distillation  yielded  yet  more  product. 


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16  - 


These  portions  were  comhlned  and  distilled  and  amounted  to  93  g. 
pure,  dry  furfural.  This  is  a yield  of  9.3'^  of  the  weight  of  the 
cobs  taken. 

Experiment  3.  - A test  showed  that  furfural  is  much  more 
soluble  in  hot  water  than  in  cold,  and  consequently,  a>mong  the 
ideal  conditions  to  be  fulfilled  by  an  apparatus  for  its  removal 
from  the  condensate,  is  the  return  of  the  separated  water  (satur- 
ated with  furfural)  to  the  flask  at  as  low  a temperature  as 
feasible.  This  condition  was  not  fulfilled  by  the  simple  trap 
(Fig.  l)  since  the  returning  condensate  was  kept  at  the  boiling 
temperature  by  the  ascending  vapor.  To  correct  this,  the  appar- 
atus sho’ifinri  in  Fig.  2 was  designed.  It  is  essentially  like  the 
former  but  has  a short  condenser  interposed  between  the  trap  and  the 
reflux  to.-cool  the-^returning  condensate  and  thus  precipitate  m.cre 
furfural.  It  is  also  provided  with  a stopcock , below  the  trap, 
thus  making  it  unnecessary  to  take  down  the  apparatus  to  obtain 
the  product.  With  this  apparatus,  the  following  experiment  was 
made : 

1 Kg.  cobs  were  distilled  with  5 L.  10*^  H5SO4  and  2 Kg.  salt 
for  11  hours. 

75  g.  of  distilled  oil  were  obtained  which  is  a yield  of  7.5f^ 
of  the  cobs  used. 

Experiment  6.  - The  apparatus  used  in  the  foregoing  experi- 
ment was  seen  to  be  inefficient  in  its  cooling  of  the  condensate, 
partly  because  of  some  steam  entering  the  lower  condenser  from 
above,  and  partly  because  of  the  warm  atmosphere  surrounding  the 
trap  which  must  necessarily  be  above  the  flask  and  burner.  To  insure 


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17 


better  cooling  of  the  ccnlensate , a water  jacket  surrounding  the 
trap  was  seen  to  be  essential.  An  apparatus  including  this  as 
well  as  other  features  was  designed  (as  shown  in  Fig.  3).  It 
consists  of  a vapor  tube  leading  to  the  top  of  a vertical  conden- 
ser of  large  capacity,  this  resulting  from  the  use  of  large  bore 
tubing  within  the  condenser  thus  offering  a large  cooling  surface. 
This  form  of  condenser  was  preferred  to  the  ordinary  narrow  tube 
type  because  of  the  prohibitive  length  of  the  latter,  cepacities 
being  equal.  The  lower  end  of  the  condenser,  v/ithin  the  water 
jacket,  formed  the  trap,  the  water  of  condensation  being  led  out 
thru  a small  tube  extending  about  5 in.  uj:  from  the  end.  This 
tube  was  bent  thru  160®  at  the  inner  end  to  prevent  globules  of 
'furfural  from  falling  into  it  and  being  carried  back  to  the  flask. 
It  was  connected  by  a small  rubber  tube  to  a point  on  the  vapor 
tube  sufficiently  high  to  maintain  a liquid  level  within  the 
condenser  about  2 in.  above  the  water  outlet  tube.  This  was  done 
to  allow  the  condensate  sufficient  time  to  become  cold  before 
returning,  and  also  to  prevent  drawdng  off  the  oil  which  collected 
on  the  surface.  In  order  to  insure  atmospheric  preseure  within 
the  apparatus,  communication  vdth  the  outside  was  established  by 
a tube  of  small  bore  extending  from  the  top  of  the  condenser  down 
within  the  water  jacket  and  connecting  to  the  inner  condenser  tubs 

at  a point  slightly  above  the  level  of  the  liquid  vdthin.  A stop- 
cock was  provided  for  the  removal  of  furfural  from  the  trap  as 

before . 

It  is  to  be  noted  that  this  form  of  condenser  is  very  compact, 
having  but  one  water  jacket,  and  the  connection  to  the  flask: is 


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- 18  - 


most  simple  and  can  be  made  with  the  greatest  ease  and  quickness. 
In  operation  it  was  also  found  to  be  very  efficient  for  the  pur- 
poses for  which  it  was  constructed.  It  was  employed  in  this  and 
remaining  experiments. 

1 Kg.  cobs  were  placed  in  the  IS-L,  flask  with  5 L.  10^  H2S04 
and  distillation  allowed  to  proceed  for  1 hr.  No  furfural  what- 
ever separated  during  this  time.  2 Kg.  salt  was  added  to  the 
mixture  and  ss  distillation  was  resumed,  furfural  began  to  collect 
at  once.  Distillation  was  contained  for  7 hrs.  luring  what  time 
crude  furfural  was  collected  as  follows: 

First  3 hrs.  - 110  g. 

Next  l-l/2«  - 30  g. 

" 2-1 /2f’  - 5 g. 

This  data  affords  some  idea  of  the  course  of  hydrolysis. 

The  product  was  v^ashed  with  a small  amount  of  lOfb  NagCOs 
solution  followed  by  water  (about  15  c.c.  of  each)  from  which  it 
was  separated  and  distilled  under  dimini  shed  pressure.  The  dis- 
solved water  with  a few  c.c.  of  furfural  was  distilled  off  at 
first,  after  which  the  pure,  dry,  pale  yellow  oil  was  brought 
over  at  110® . 

Yield  - 124  g.  12.4  ^ of  cobs  used. 

Experiment  7.  - This  run  was  a check  on  Exp.  . 6 and  was  -made 
essentially  the  same. 

1 Kg,  cobs  were  distilled  for  6-1/4  hrs.  with  10^  HgS04  and 
salt  as  before.  Cru.de  furfural  was  collected  as  follows: 


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“ 19 


First  2-3/4  hrs. 

120 

Next  hour 

20 

S* 

« 2-1/2  hrs. 

10 

g* 

The  proluct  \7as  neutralized  and  washed  as  before  and  dis- 
tilled  at  100©,  almost  colorless. 

Yield  - 133  g.  = 13.2^  of  cobs. 

Experiment  8.  - It  was  desired  to  learn  if  the  action  of 
the  salt  'was  merely  physical  (salting  out)  or  chemical,  since  it 
is  well  knovrai  that  a boiling  solution  of  HgSO^  and  NaCl  must  con 
tain  HCl  also,  and  it  was  of  interest  to  know  if  the  presence  of 
the  KCl  was  essential  or  ad‘'/antageous . 

In  thias  exp^sriment,  the  salt  was  replaced  with  NasSO^  and 
the  distillation  performed  as  before.  Mo  furfural  could  be 
obtained.  This  was  later  explained  by  the  neutralization  of  the 
H2SO4  present  to  form  NaHSC^  which,  apparently,  did  not  furnish 
sufficient  acid  concentration  to  effect  hydrolysis. 

Experiment  9.  - To  eliminate  the  above  difficulty,  this 
run  was  made  with  the  acid  sulfate. 

1 Kg.  cobs  were  distilled  for  8 hrs.  with  5 L.  10^  HgS0  4 
and  3 Kg.  KHSO4  (MaH804  was  not  obtainable)  . A larger  amount 
of  the  acid  sulfate  was  used  than  when  salt  was  employed,  partly 
because  of  its  greater  solubility  making  it  possible,  and  partly 
tc  make  the ' comparison  favorable  to  the  acid  sulfate.  Crude 
furfural  was  collected  as  follows: 

First  3 hrs.  - 55  g. 

Next  5 ” - 25  g. 


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- 20  - 


Yield  of  distilled  product  - 73  g»  * 7,3^^  of  cobs. 

Exceriment  10.  - In  order  to  determine  the  effect  of  varying 
the  acid  concentration,  this  and  the  next  experiment  were  performed 
using  30v^  and  H-SO4  respectively. 

1 Kg,  cobs  were  distilled  4 hrs.  v7ith  5 L,  20f5  H2SO4  and 
2 Kg,  salt,  75  g,  of  crude  furfural  was  collected  during  the  first 
2-1 /2  hrs.  after  which  no  more  could  be  obtained.  Much  more 
rapid  carbonization  of  the  cobs  occurred  than  when  10^^  acid  was 
used,  and  much  foaming  ensued  which  necessitated  distilling  at  a 
very  reduced  speed.  In  spite  of  this,  furfural  was  evolved  quite 
rapidly,  more  rapi dly, apparently,  than  in  any  previous  in;in. 

Yield  - 62  g.  = 6.2 

Experiment  11,  - 1 Kg.  cobs  were  distilled  with  5 L,  5^- 
K2S04  and  2 Kg,  salt  for  a period  of  6 hrs.  At  the  end  of  this 
time,  oil  was  still  being  evolved  but  a break  in  the  condenser 
caused  the  discontinuance  of  the  experiment.  Crude  furfural  was 
collected  as  follows; 

\ 

First  2 hrs.  - 52  g. 

Next  1-1/2”  - 43  g, 

” 4-1/2”  - 55  g. 

This  was  neutralized,  washed  and  distilled  and  gave  a yield 
of  125  g.  = 12.5^. 


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- 21 


NOTES 

One  remarkable  feature  of  the  prepa.ration  of  furfural  by 
hydrolysis,  is  the  unusual  purity  of  the  crude  product.  Distilled 
from  a heterogeneous  mixture  of  unknown  comp.osition,  the  oil  may 
be  almost  completrely  distilled  over  a range  of  1 or  2 degrees, 
only  a trace  of  high  boiling  residues  remaining. 

Another  interesting  point  in  connection  'Alth  the  purity  of 
furfural  is,  that,  altho  it  may  be  quits  colorless  when  distilled, 
it  often  darkens  and  becom.es  black  on  standing  a few  v/seks,  or 
sometim.es  even  a few  hours.  This  blackening  is  probably  due  to 
decomposition  of  associated  impurities  with  form;ation  of  colloidal 
carbon.  The  tendency  to  blacken  seems  to  be  largely  influenced  by 
the  temperature  of  distillation,  consequently  vacuum  distillation 
is  advised.  I discovered  that  furfural  dried  over  CaCls,  bladkened 
over  night  and  this  led  m.e  to  suspect  that  the  presence  of  acid 
on  distillation  was  an  important  factor.  And  I found  that  neutral- 
ization of  the  oil  before  distille.tion  greatly  increased  its 
stability  in  respect  to  color.  Some  so  distilled  has  thus  far 
as3um»ed  only  a golden  color  after  two  weeks  standing,  altho  it 

was  distilled  at  a relatively  hish  temperature  (ilOo ) . 

(12) 

Beilstein  gives  a method  of  purification  which  consists 
of  treating  the  crude  oil  with  small  amiounts  cf  chromic  acid  to 
oxidize  impurity.  It  would  be  interesting  to  learn  how  this 

treatment  would  affect  the  tendency  of  the  furfural  to  bla.cken. 


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- 22  - 

Another  Possible  ATp-plicatlon  of  the  Method. 

Because  of  the  greater  speed  of  hydrolysis  and  the  probable 
increase  in  furfural  yield,  it  seems  quite  reasonable  to  expect 
that  this  new  method  fcr  furfural  production  'will  have  wide 
application  in  the  analytical  field  and  appreciably  alter  the 
existing  methods  for  determination  of  ppentoses,  pentosans,  oxy- 
cellulose,  etc.  It  has  been  impossible  in  this  research  because 
of  the  limited  time  at  disposal,  to  attempt  experiments  along 
this  line . 

COTJCLUSION . 

A study  of  the  experimental  data  makes  the  follovdng  points 
seem  essential  to  the  preparation  of  furfural  if  the  maximum 
yield  is  to  be  obtained. 

l)  The  acid  concentration  should  be  as  low  as  possible,, 
economy  of  acid  being  balanced  against  economy  of  time.  I have 
shown  that  high  acid  strengths,  altho  it  may  increase  the  rate 
of  hydrolysis,  tends  toward  a low  yield,  and  I believe  that 
somewhere  between  sf?  and  IS'^-  lies  the  optimum  concentration. 

3)  The  returning  furfural  solution  should  be  cold  in  order 
to  return  as  little  furfural  as  possible, 

3)  The  returning  solution  should  pass  down  the  tube  up 
which  the  hot  vapors  are  rising.  This  has  the  tendency  to  steam 
distil  the  product  from  the  returning  -water  and  concentrate  it 
in  the  condenser.  The  low  yield  in  Exp,  5,  indicates  this,  and  I 
also  h-ave  observed  in  the  operation  of  the  condenser  in  Expts,  6- 


- 23 


11  that,  aftar  drawing  off  oil  from  the  trap  v»rhile  the  distillatioi| 
was  in  progress,  the  rate  of  furfural  separation  was  greatly 
diminished,  undoubtedly  due  to  the  temporary  cessation  in  the 
flov/  of  returning  solution  resulting  from  lowering  the  level  in 
the  trap. 

4)  The  presence  of  a salt  is  quite  essential  to  the  oper- 
ation of  the  method  as  shewn  in  Extp  . 6.  KHSO4  may  be  used  in 
place  of  NaCl  in  the  cob-acid  mixture,  but  does  not  seem  to  be 
as  satisfactory.  This  would  indicate  that  HCl  is  a more  satis- 
factory hydrolytic  agent  than  HgSO^.  The  use  of  KCl  and  NaCl 

to  the  total  exclusion  of  would  probably  give  quite  satis- 

factory results.  However,  the  elimination  of  KCl  might  be  desir- 
able in  the  technical  manufacture  of  furfural  where  copper  or 
other  metallic  condensers  were  employed,  because  of  the  volatility 
of  this  acid. 

5)  Because  of  the  volatility  of  KCl  and  the  formation  of 
volatile  organic  acids,  (acetic,  etc.)  during  hydrolysi s,  the 
crude  furfural  -will  always  be  found  acidic.  I have  shown  that 
it  is  desirable  to  neutralize  these  acids  and  leave  the  product 
slightly  alkaline  on  distillation  if  the  color  is  to  be  preserved. 

SUMMARY 

1)  A theory  has  been  developed  concerning  the  rats  of 
formation  and  decomposition  of  furfural  in  sulfuric  acid  solution. 

2)  A method  has  been  worked  out  for  the  preparation  of 
furfural  which  is  practically  automatic  in  regard  to  labor; 


24  - 


7/hich  is  more  eoonomical  in  regard  to  chemical  consumption,  re- 
quires less  time,  and  is  capable  of  giving  a larger  yield  than 
any  previously  existing  method* 

3)  Several  types  of  apparatus  have  been  constructed  and 
data  obtained  from  each  in  operation.  From  this  data,  conclusions 
have  been  dravm  which  may  serve  as  a godde  in  the  operation  of 
the  method,  both  on  a laboratory”  scale  and  commercially. 

4)  The  effects  of  varying  two  important  conditions  of  the 
process,  namely,  concentration  of  acid  and  kind  of  salt  used,  have 
been  studied  . 

5)  One  cause  of  the  discoloration  of  freshly  distilled 
furfural  has  been  determined. 


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BIBLIOaHAPHY 

l)  Organic  Chemistry  - 1-269 
V (C.  Nagel  - Wochschr.  Branw  - 30-345 
(K.  Forster  - Ber.  - 15-230,323 

3)  Papierfahr.  - 12-1040 

4)  Dobereiner  - Ann. -3-141 

5)  Fovmes  - Ann,  54-52 

6)  Z.  Physiol.  Chem . -50-209 

7)  Cross  and  Sevan  - Papermaking  - 21 

b)  Thorpe  - 708 

9)  Babo  - Ann.-  85  - 100 

10)  Allen  - 1-400 

11)  Zeitsch.-  Angsw.Chem.  27-654 

12)  Handbuch  - 3-731 

13)  Ber.  - 34  - 3019 

14)  Lab,  Man.  - 190 


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